For over 1500 years, Ancestral Pueblo people built and used underground rooms. Archaeologists distinguish pithouses and kivas by their different roofing systems: pithouses, used from about 300 before common era to 1100 common era, supported roofs with four upright posts, while kivas, built from about 1000 common era to 1280 common era, used stone pillars called pilasters around the room's perimeter to support the roof. Because this structure has six pilasters around the perimeter supporting the roof, it is a kiva. Like a pithouse, a kiva served daily activities such as cooking, craftwork, sleeping, and socializing, while providing warm shelter in winter and a cool retreat in summer. Kivas were entered and exited through the roof by ladder, and their features included a ventilator shaft that drew fresh air down into the room, a cribbed roof made from layered beams covered with brush and earth to form a flat roof at ground level, a subfloor vent connecting to the ventilator shaft, a central hearth for heat, light, and cooking, and a floor vault whose purpose is uncertain but may have been used for storage or covered with wood planks for use as a foot drum.